17 research outputs found
Scalar diquark in top-antitop production and constraints on Yukawa sector of grand unified theories
International audienceA colored weak singlet scalar state with hypercharge 4/3 is one of the possible candidates for the explanation of the unexpectedly large forward-backward asymmetry in tt production as measured by the CDF and D0 experiments. We investigate the role of this state in a plethora of flavor chang- ing neutral current processes and precision observables of down-quarks and charged leptons. Our analysis includes tree- and loop-level mediated observables in the K and B systems, the charged lepton sector, as well as the Z → b ¯b width. We perform a fit of the relevant scalar couplings. This approach can explain the (g − 2)µ anomaly while tensions among the CP violating observables in the quark sector, most notably the nonstandard CP phase (and width difference) in the Bs system cannot be fully relaxed. The results are interpreted in a class of GUT models which allow for a light colored scalar with a mass below 1 TeV
On the flavor structure of the littlest Higgs model
We investigate the Yukawa sector for up-like quarks in the Lee's version of
the Littlest Higgs model. We derive general quark mass and mixing formulae and
study leading order contributions due to non-zero light quark masses. Relying
on the unitarity of the generalized quark mixing matrix we obtain corrections
to the CKM matrix elements. In this model FCNCs appear at the tree level and
using leading order contributions we obtain the FCNC couplings for the up-like
quark transitions. In light of recent experimental results on the D0 - D0bar
transition we make predictions for xD as well as the D to mu+ mu- decay rate.
Finally, we discuss probabilities for the t to c (u) Z transitions relevant for
the LHC studies.Comment: 6 pages, 1 figur
Chiral behavior of the B(s,d)-Bbar(s,d) mixing amplitude in the Standard Model and beyond
We compute the chiral logarithmic corrections to the Bd and Bs mixing
amplitudes in the Standard Model and beyond. We then investigate the impact of
the inclusion of the lowest-lying scalar heavy-light states to the decay
constants and bag-parameters and show that this does not modify the pion chiral
logarithms, but it does produce corrections which are competitive in size with
the K- and eta-meson chiral logarithms. This conclusion is highly relevant to
the lattice studies since the pion chiral logarithms represent the most
important effect in guiding the chiral extrapolations of the lattice data for
these quantities. Also important is to stress that the pion chiral logarithmic
corrections are useful in guiding those extrapolations as long as Mpi << Delta,
where Delta is the mass gap between the scalar and pseudoscalar heavy-light
mesons.Comment: 16 pages, 5 figures (published version
Physics of leptoquarks in precision experiments and at particle colliders
We present a comprehensive review of physics effects generated by leptoquarks
(LQs), i.e., hypothetical particles that can turn quarks into leptons and vice
versa, of either scalar or vector nature. These considerations include
discussion of possible completions of the Standard Model that contain LQ
fields. The main focus of the review is on those LQ scenarios that are not
problematic with regard to proton stability. We accordingly concentrate on the
phenomenology of light leptoquarks that is relevant for precision experiments
and particle colliders. Important constraints on LQ interactions with matter
are derived from precision low-energy observables such as electric dipole
moments, (g-2) of charged leptons, atomic parity violation, neutral meson
mixing, Kaon, B, and D meson decays, etc. We provide a general analysis of
indirect constraints on the strength of LQ interactions with the quarks and
leptons to make statements that are as model independent as possible. We
address complementary constraints that originate from electroweak precision
measurements, top, and Higgs physics. The Higgs physics analysis we present
covers not only the most recent but also expected results from the Large Hadron
Collider (LHC). We finally discuss direct LQ searches. Current experimental
situation is summarized and self-consistency of assumptions that go into
existing accelerator-based searches is discussed. A progress in making
next-to-leading order predictions for both pair and single LQ productions at
colliders is also outlined.Comment: 136 pages, 22 figures, typographical errors fixed, the Physics
Reports versio
Constraining Higgs mediated dark matter interactions
31 pages, 9 figuresWe perform an analysis of Higgs portal models of dark matter (DM), where DM is light enough to contribute to invisible Higgs decays. Using effective field theory we show that DM can be a thermal relic only if there are additional light particles present with masses below a few 100 GeV. We give three concrete examples of viable Higgs portal models of light DM: (i) the SM extended by DM scalar along with an electroweak triplet and a singlet, (ii) a Two Higgs Doublet Model of type II with additional scalar DM, (iii) SM with DM and an extra scalar singlet that is lighter than DM. In all three examples the Br(h to invisible) constraint is not too restrictive, because it is governed by different parameters than the relic abundance. Additional light particles can have implications for flavor violation and collider searches
Les Houches 2017: Physics at TeV Colliders New Physics Working Group Report
International audienceWe present the activities of the `New Physics' working group for the `Physics at TeV Colliders' workshop (Les Houches, France, 5--23 June, 2017). Our report includes new physics studies connected with the Higgs boson and its properties, direct search strategies, reinterpretation of the LHC results in the building of viable models and new computational tool developments